Patent Literature 1 and FIG. 9 show an example of a capacitive pressure sensor that is used in measuring, for example, the pressure of a gas in a semiconductor manufacturing process or other processes, and in which consideration is given to thermal deformation.
That is, a capacitive pressure sensor 100A illustrated in FIG. 9 includes a body 1A, a diaphragm 2A, an electrode member 3AA, and an insulating positioning member 4A. The body 1A is substantially cylindrical, and is made of a metal such as stainless steel. The diaphragm 2A is joined to and blocks one end of the body 1A. The electrode member 3AA has an electrode face 3SA opposed to and a predetermined gap apart from the diaphragm 2A. The insulating positioning member 4A made of a glass, ceramic, or other materials is supported by the body 1A, and positions the electrode member 3AA in the body 1A.
The insulating positioning member 4A has a shape of a substantially solid dual cylinder projecting toward the diaphragm 2A. One of the cylindrical portions of the insulating positioning member 4A is supported by a support part 11A that is ring-shaped and projects toward the inside of the body 1A. Moreover, the other cylindrical portion of the insulating positioning member 4A projects toward the diaphragm 2A, and is closer to the diaphragm 2A than the support part 11A. The electrode face 3SA, which is the end face of the other cylindrical portion, is provided near and the predetermined gap apart from the diaphragm 2A. Moreover, to keep the gap constant, the insulating positioning member 4A is pressed in the direction vertical to the diaphragm 2A.
However, in such a structure of the insulating positioning member 4A, when thermal deformation of the capacitive pressure sensor 100A occurs in response to a change in temperature, the position of the electrode face 3SA in the direction parallel to the diaphragm 2A cannot be prevented from deviating from the position of the diaphragm 2A. For instance, if the center of the electrode face 3SA does not match the center of the diaphragm 2A, the electrode face 3SA mainly refers to a place in the diaphragm 2A where deformation is less likely to occur than in the center. Thus, the electrode face 3SA detects a smaller change in capacitance than under the normal conditions. Moreover, the measurement of the capacitance is affected by, for example, a difference in the plane roughness of the diaphragm 2A between a portion referred to by the electrode face 3SA under the normal conditions and a portion referred to by the electrode face 3SA when the deviation occurred.
Thus, the deviation of the position of the electrode face 3SA in the direction parallel to the diaphragm 2A from the position of the diaphragm 2A causes a change in capacitance not due to pressure, thereby decreasing the measurement accuracy of the pressure.
There is another problem described below. In such a structure of the insulating positioning member 4A, if thermal deformation of the capacitive pressure sensor 100A occurs in response to a change in temperature, the gap between the diaphragm 2A and the electrode face 3SA significantly deviates from a predetermined value, thereby decreasing the measurement accuracy of the pressure.
The cause of the deviation will be described with a specific example in which there has been an increase in temperature in the capacitive pressure sensor 100A. In the capacitive pressure sensor 100A in FIG. 9, the other cylindrical portion of the insulating positioning member 4A projects from the same horizontal position as the position at which the insulating positioning member 4A is supported by the body 1A, toward the diaphragm 2A. The thickness of the support part 11A of the body 1A between the diaphragm 2A and the top of the support part 11A is substantially the same as that of the insulating positioning member 4A between the diaphragm 2A and the top of the support part 11A. While the support part 11A made of the metal expands with an increase in temperature, the other cylindrical portion of the insulating positioning member 4A made of the glass or ceramic hardly deforms. Thus, this increases the gap between the diaphragm 2A and the electrode face 3SA.